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Global warming may drive more active La Niña pattern

Broad tree-ring record provides accurate ENSO history

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Researchers say tree ring records show that El Niño activity during the 20th century has largely been outside the range of natural variability.

By Summit Voice

Climate scientists have long suspected that global warming has an influence on the Pacific Ocean El Niño- La Niña cycle (El Niño-Southern Oscillation), but instrumental records tracking the shift between above- and below average sea surface temperatures don’t go back far enough to provide context for any recent changes in the pattern.

But scientists working at the International Pacific Research Center, University of Hawaii at Manoa say a new tree ring record extending back about 700 years has helped decipher long-term trends. The tree ring samples from both the tropics and mid-latitudes in both hemispheres support the idea that the unusually high ENSO activity in the late 20th century is a footprint of global warming said Jinbao Li, lead author of the study published online in the journal Nature Climate Change. Continue reading

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Climate: For El Niño, timing is everything

Study identifies wind patterns that could lead to better El Niño forecasts

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El Niño affects global weather patterns.

By Summit Voice

SUMMIT COUNTY — Climate researcher say they’ve discovered an atmospheric pattern that helps explain why El Niño often peaks during the first part of winter and usually fades away in late winter and early spring.

El Niño phases are part of a cycle when sea surface temperatures in the equatorial Pacific Ocean are warmer than average. The various phases of the so-called ENSO can have pronounced impacts on weather around the globe, spurring droughts in some areas and flooding in others.

The new study from the University of Hawai’i at Manoa Meteorology Department and International Pacific Research Center identified an unusual wind pattern that straddles the equatorial Pacific during strong El Niño events and swings back and forth with a period of 15 months as a key driver in the annual cycle. The findings were reported in the May 26 online issue of Nature Geoscience. Continue reading

Report: Global warming not a big factor in 2012 drought

Natural climate variability the biggest player, scientists say

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Drought conditions persist across the central part of the country.

By Bob Berwyn

SUMMIT COUNTY — Last summer’s crippling Great Plains drought can’t definitively be linked with global warming, according to a team of federal scientists from various agencies. In a new report issued this week, the researchers said the drought was probably caused by a confluence of natural climate variations that might only come together in a similar constellation once a century.

Cyclical variations in ocean temperatures — especially the combination of a cooler-than-average Pacific Ocean and a warm phase of the North Atlantic Multidecadal Oscillation may have nudged the region toward drought conditions, but those factors tend to be more of a factor in suppressing winter precipitation. Continue reading

Colorado: No El Niño, no La Niña – what’s driving the weather?

Spring outlook trends toward warm and dry conditions

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The Madden-Julian Oscillation has played a role in Colorado weather this winter.

By Summit Voice

FRISCO — With neither El Niño or a La Niña conditions in the Pacific Ocean, long-range weather forecasters have been struggling to develop confidence in their outlook for the coming spring season — a critical time for much of the West in terms of getting some relief from drought conditions.

A wet and cool spring could at least take the edge off the drought in some areas, helping to maintain stream flows and reduce the potential for massive and dangerous wildfires. Conversely, a return to last year’s very dry and warm spring pattern would spell trouble for places like Colorado.

So if the El Niño-La Niña cycle isn’t driving the weather, what is? What we do know is that conditions over the Pacific Ocean are the key to understanding exactly what path storms will take across the western United States, and that conditions in the North Atlantic can also be a factor. Continue reading

New study helps pinpoint El Niño impacts

Findings could help improve long-range winter forecasts

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Shifting cycles of warmer and cooler water in the central Pacific influence weather patterns around the world.

By Summit Voice

FRISCO — A new study that sorts El Niño events into two categories could help forecasters develop better long-range forecasts to predict how the periodic warming of equatorial East Pacific waters may affect winter weather.

Part of the data for the research came from an array of buoys across the Pacific called the TAO-Triton array. The buoys observes conditions in the upper ocean to forecast El Niño months in advance, and for monitoring it as it grows and decays.

After analyzing all El Niño events since 1979, the NOAA and University of Washington scientists said the El Niños that show a drop in outgoing long-wave radiation from the tops of deep convective clouds are the ones that tend to play havoc with winter weathers. Continue reading

Study finds link between El Niño and warming along the Antarctic Peninsula during parts of the Holocene

Ocean-driven warming along western Antarctic Peninsula may be partly driven by natural climate variability

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Ice remnants along the shore of the Antarctic Peninsula. Bob Berwyn photo.

By Summit Voice

SUMMIT COUNTY — Temperature oscillations in the tropical Pacific have historically had a significant effect on the climate of the western Antarctic Peninsula, according to scientists who studied a 12,000-year fossil record to measure how much glacial ice melted into the sea during that span.

The research is important because the western Antarctic Peninsula is one of the fastest warming regions on the planet, and the fastest warming part of the Southern Hemisphere. The ice sheets of the region may be vulnerable to collapse, and would raise sea level by several meters if the melt.

The study, led by Cardiff University researchers, measured oxygen isotopes in microscopic marine algae fossils to trace glacial ice entering the ocean along the western Antarctic Peninsula. Based on the data, the study concluded that the atmospheric temperatures had a bigger factor than oceanic circulation on warming along the western Antarctic Peninsula than oceanic circulation in the late Holocene (from 3,500-250 years ago). Continue reading

New coral data traces 7,000 years of El Niño history

20th century oscillations show intensification that may be linked with global warming

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A NOAA graphic showing early January 2012 ocean surface temperature anomalies.

By Summit Voice

SUMMIT COUNTY — Atmospheric scientists say they’ve used coral records to trace the history of El Niño cycles going back about 7.000 years, showing that 20th century oscillations  are much stronger than those captured in the fossil record.

But the study also showed large natural variations in past ENSO strength, making it difficult to attribute the 20th century intensification of ENSO to rising carbon dioxide levels. Such large natural fluctuations in ENSO activity are also apparent in multi-century climate model simulations, but the 20th century intensification stands out as statistically significant and could be linked with global warming.

The new information will help assess the accuracy of climate model projections for 21st century climate change in the tropical Pacific. Continue reading

Climate: Parts of the tropical Pacific Ocean are shifting toward a permanent El Niño-like pattern

Archived ocean observations help create new data set for climate models

Atmospheric circulation patterns drive convection in the tropics and can have a far-reaching effect on global climate. Bob Berwyn photo.

By Summit Voice

SUMMIT COUNTY — A new set of more complete sea surface temperature data has helped scientists explain a gradual, decades-long slowdown of a key tropical atmospheric circulation, linking it with the steady increase in global temperatures during the past few decades.

“Our experiments show that the main driver of the change in the Walker circulation is the gradual change that has taken place in the surface temperature pattern toward a more El Niño-like state,” said Hiroki Tokinaga, associate researcher at the International Pacific Research Center, University of Hawaii at Manoa. “We don’t have enough data yet to say to what degree the slowdown over the last 60 years is due to a rise in man-made greenhouse gases or to natural cycles in the climate,” Tokinaga said.

The Walker circulation determines much of the tropical Indo-Pacific climate and has a global impact as seen in the floods and droughts spawned by the El Niño-Southern Oscillation. Meteorological observations over the last 60 years show this atmospheric circulation has slowed: the trade winds have weakened and rainfall has shifted eastward toward the central Pacific. Continue reading

Climate: NOAA drops El Niño watch

Forecasters call for neutral conditions, but say a La Niña is not out of the question

n El Niño never managed to establish itself in the equatorial Pacific this year.

The three-month precipitation outlook from NOAA’s Climate Prediction Center.

By Summit Voice

FRISCO — With sea surface temps cooling to near average in much of the equatorial Pacific, NOAA’s Climate Prediction Center has dropped an El Niño watch that’s been in effect for the past several months.

El Niño is part of a cyclical pattern of sea surface temperature variations that affects global weather patterns. The emerging El Niño forecast last spring and summer offered some hope for drought relief in the parched Southwest and the southern tier of states, where warmer than average Pacific Ocean temps can help boost winter and spring precipitation.

During La Niña years, when cooler-than-average sea surface temperatures prevail in the same region, the storm track often shifts northward, driving storms into the Pacific Northwest and then down across the northern Rockies and northwest Colorado. Continue reading

Colorado: Finally, some snow in the forecast

Weather change coming, details uncertain

A Gulf of Alaska low will start to move toward western Colorado later this week.

By Summit Voice

SUMMIT COUNTY — All those snow dances and sacrificial bonfires could pay off late this week as the weather pattern across North America looks to flip-flop, with high pressure in the West giving way to a broad Pacific trough that promises to bring widespread precipitation to the region.

But it’s too early to tell exactly where the snow will fall. For now, the forecast models are predicting that a vigorous cold front will cross Colorado Friday night into Saturday, bringing the best chance for snow. Continue reading

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